Portable grinding mill



Nov. 8, 1960 J. G. RIMMER 2,959,363

PORTABLE GRINDING MILL Filed Jahe, 1956 4 Sheets-Sheet 1 51 4 JamcsGlRz'mmev;

BYWWQW Nov. 8, 1960 J. G. RIMMER PORTABLE GRINDING MILL Filed Jan. 6, 1956 4 Sheets-Sheet 2 INVENTOR. James Gifiz'mmm;

01W flaw/Z NOV. 8, 1960 RlMMER 2,959,363

PORTABLE GRINDING MILL Filed Jan. 6, 1956 4 Sheets-Sheet 3 Q00 03 C N m $6 m l gig am, 67%;, g 5' Nov. 8, 1960 J. G. RIMMER PORTABLE GRINDING MILL.

4 Sheets-Sheet 4 Filed Jan. 6, 1956 United States Patetlt'O PORTABLE GRINDING MILL James G. Rimmer, Madison College, Madison, Tenn. Filed Jan. 6, 1956, Ser. No. 557,719

16 Claims. (Cl. 241-81) This invention relates to a grinding mill and more particularly to a portable grinding mill adjustable to produce ground grain products of varying finenesses regardless of the size or hardness of the grains introduced to the mill.

A very important object of this invention is to provide a portable mill for grinding grains of different sizes, either individually or mixed, to produce any desired uniform size of ground product.

Another object of this invention is to provide a portable grinding mill provided with a differential impeller having two or more grooves of different depths, the deeper grooves being adapted to feed both large and small grains to the grinding burrs, and the shallower grooves being adapted to feed the smaller grains only.

A further object of this invention is to provide a portable grinding mill having a novel lubricating system.

Another object of this invention is to provide a portable grinding mill having its impeller shaft inclined to the horizontal.

Another object of this invention is to provide a portable grinding mill having means for adjusting the fineness of the ground product.

A further object of this invention is to provide a portable grinding mill in which heat generated by the operating parts is rapidly disseminated and the grinding chamher is well-ventilated.

Another object of this invention is to provide a lubricating system in which the impeller shaft and drive shaft are inclined to permit the gears and hearings to operate in an oil bath without leakage or dripping.

Another object of this invention is to provide a portable grinding mill which is of compact, simple and Wellbalanced construction, and may be safely, easily, automatically and economically operated.

Further objects and advantages of the invention will be apparent from the following description taken in conjunction With the drawings, wherein:

Fig. 1 is an elevational view in section taken along the line 11 in Fig. 3.

Fig. 2 is an elevational view of the mill covering substantially the same area as Fig. 1.

Fig. 3 is a side elevation of the mill with a partial transverse section along line 3-3 of Fig. 1.

Figs. 4, 5, 6, respectively, are detail views of the lever 4 of Fig. 1, the thrust ball-bearing, and part of the shaft which is moved endwise thereby.

Fig. 7 is a side view of the impeller and hub in partial section through the grinding burr and drive flange, taken on line 7-7 of Fig. 8.

Fig. 8 is a partial right-end view of Fig. 7.

Fig. 9 is a partial face view of -a grinding burr showing some of the teeth and other details.

Fig. 10 is a side view of the selective impeller with its flange, in partial section on line 10-10 of Fig. 11.

Fig. 11 is a left-end view of the selective impeller.

Fig. 12 is a supplementary and partly sectional view similar to Fig. 7, but showing a special groove in the selective impeller.

recess 6 (106) in lever 4.

Fig. 13 is an edge view of a grinding burr showing a part of the teeth and flour grooves.

Fig. 14 is a plan view of the switch and thermocontrol box.

Fig. 15 is an enlarged sectional elevational view of a modification of the lever assembly disclosed in Fig. 1.

Fig. 16 is an exploded side-view of the adjustment knob of Fig. 15 with the calibrated sleeve and Washer in section.

Fig. 17 is a side view of the calibrated sleeve 111 of Figs. 15 and 16.

Fig. 18 is a sectional view of a modification of the shaft and impeller disclosed in Fig. 1'.

Fig. 19 is an enlargement of the central structure of Fig. 18.

In Figs. 1 and 15, the housing 1 (or 1') encloses a spiral drive gear 2 (102) fixed on an inclined shaft 3 (103) adapted to be axially adjustable by means of a lever 4 (104) of the second order. crum is provided by a threaded rod 4a (104a) having a rounded tapered end 5 (105) universally supported in In Fig. 15, a small pin 104b is provided at the end of the tapered end of 105 to register freely in a hole in the closed end of the recess 106.

Rod 4a (104a) is adjustable to correct its working position in the threaded boss 7 (107) of housing 1 (1) and is secured by locknut 8 (104a). A micrometer-style of threaded rod 9 (109) operating in housing boss 10 (110) has a threaded hub 16 (116) with a locknut 17 (117, 117b) at one or each end of the hub and a suitable knurled flange 15 for a hand grip at its outer end, and a rotatable barrel or calibrated sleeve 11 (111) suitably marked with longitudinal lines 12 (112) and progressive figures 13 (113), as disclosed in Figs. 2 and 17. The barrel 111 may be set independently of the hub 116 by tightening screws 111b which co-operate with the washer 111a through tapped holes, whereby the sleeve 111 may be gripped between washer 111a and flange 115. By rotating the calibrated sleeve 11, the appropriate line 12 may be registered with the indicator 14 in order to obtain the desired fineness of the ground product. The barrel 111 may be smoothly finished between lines and is preferably of non-rusting material, so that easily removable pencil marks or such notations may be made thereon, thus facilitating future settings.

The lever 4 (104) has two suitably rounded projections 18 (118), Figs. 1, 46 and 15, abutting truly against the thrust bearing plate 20 (120) supporting the ballbearings 19 (119), such action being facilitated by the swivel fulcrum 5 (105) in recess 6 (106) and the simple arrangement for non-deviating pressure against lever 4 (104) by the rounded end of the micrometer style of screw 9 (109) against the end 21 (121). Thus, the lever 4 (104) is Well adapted to exert even pressure on and to move thrust ball-bearings 19 (119) the minute amount required in a precision grinding mill of this type. The thrust ball-bearings 19 (119) move gear hub 22 (122) integral with spiral gear 2 (102), and consequently raise shaft 3 (103) when the sleeve 11 (111) and micrometer-type screw 9 (109) are rotated in one direction, While reverse rotation of screw 9 (109) permits axial lowering of the shaft 3 (103) by virtue of gravity and the rotation of the spiral gear 27. A stop screw with a locknut 23 limits the backward travel of lever 4 to prevent disengagement of the gears 2 and 27, in Fig. 1. In Fig. 15, a screw 123 held in desired adjustment by locknut 123a provides a similar function as well as preventing destructive interengagement of the grinding burrs 45 and 45.

The housing 1 is provided with a general oil bath for the internal mechanism contained therein. A threaded plug 24 having suitable ventilating channels (not shown) An adjustable fultherein serves as an oil-filling-hole plug and prevents air pressure building up in housing due to temperature changes. Oil plug 25 in Fig. 2 is an oil-height indicator, and oil plug 26, Fig. 2 is an oil drain plug. In Fig. 3 the spiral gear 2 is in driven engagement with a co-operating driving spiral gear 27 fixed on shaft 28, which is journaled at 29 and 30 (Fig. 3). Between the spiral gear 27 and bearing 29 is located a thrust ball-bearing 31. A movable collar 32 with set screw 32 permits snug endwise permanent adjustment of shaft 28 between bearing 33 and thrust ball-bearing 31, thus enabling thrust ballbearing 31 to function precisely in resisting the driving thrust of spiral gear 27 on spiral gear 2 (Figs. 1 and 3).

Registered into and forming a cover for the housing 1 at 34 and secured thereto by suitable means, such as cap screws 35, 35', 35", is a flange 36 integral with a bearing body 37. At the opposite end of the body 37 is another flange 38 which registers into the ventilated grinding chamber 39. On flange 38 may be a cover plate 40 fitted with packing material 40' to exclude particles of foreign matter from the journal bearing and from the return oil channel 42 which leads into the interior of housing 1. The bushing 41 of the bearing journal may well be of the porous-bronze oil-containing and metering type, which does not encourage the dripping of oil, and this feature with the oil-return channel 42 on the angle tends to eliminate all oil drip into the grinding chamber 52 or into the ground product being produced by the mill. The journal bearing bushing 41 may have a shallow oil reservoir (not shown) all or partially around it and connected with an oiling opening closed by plug 43.

The considerable external air-space 44 (Fig. 2) between flange 36 and flange 38 prevents most of the heat generated by the mechanism in housing 1 from passing to the ventilated grinding chamber 39, an important feature in the plan of the grinding mill.

Also shown in Figs. 2 and 3 is a readily demountable ventilated chamber 39, which houses the two similar grinding burrs 45 and 45'. The burr 45 is snugly fitted into a recess on the inside of chamber 39 at 46 and fixed therein by suitable bolts and nuts 47. Burr 45 is likewise seated in and secured to a recessed driving flange 48, which has on the side opposite from the attached burr 45 a preferably integral center boss 49, the whole being mounted in concentric relationship to shaft 3. A suitable driving means such as a screw or a driving pin 50, preferably readily removable and supplied with a simple lock means 51 (Figs. 7, 8) to hold it in driving position, penetrates the boss 49 and shaft 3 providing driving relationship from shaft 3 to boss 49 and thus to flange I plate 48 and burr 45. The grinding chamber 39, in order to prevent an accumulation of heat from the action of the burrs on the grist and in other ways, is ventilated through suitably arranged openings 52 (Figs. 1 and 2).

This ventilation of the grinding chamber is important to the successful operation of the mill. The large groundproduct outlet 53 (Figs. 1, 2 and 3) in the lower part of the grinding chamber 39 furnishes ample air inlet for the needed ventilation just described, and this ventilation together with the large air spaces between housing l, the electric motor 54 and the grinding chamber 39, helps to prevent the passage to, and the accumulation of heat in the grinding chamber 39 where it would be most detrimental to the operation of the mill. With the proper placing and proportioning of all parts of the mill and with adequate ventilation as described herein, well-dried grains, even including those with the largest and hardest kernels, may be ground continuously for as long as required without trouble, even in hot weather. The grinding chamber 39 is registered with flange 38 at 65 and is secured in position by bolts 66, one being shown in Fig. 2 and both in Fig. 3.

The hopper 56, preferably of one-piece construction and rectangular shape, is so formed that an upward extension made of some light material such as stout cardboard or light ply-wood may be, if required, easily prepared and fitted thereto. The hopper 56 preferably has at least one of its walls steeply sloped (at an angle of the order of 60) so as to prevent the feeding grain from arching over the outlet and blocking the flow. Hopper 56 feeds the grist through an orifice 57 into a ferrous-metal, T-shaped receptacle 58. The bottom of receptacle 58 is provided with a removable plug having a handling knob 60, and adapted to be secured in closed position by means such as screws 61 and 61'. By releasing the screws 61 and 61' and removing the plug 59, unused grist may be discharged from the hopper 56. The T 58 is equally bored with the grinding chamber wall at 62 to provide, when aflixed together at 63, a smooth passageway or tunnel. The T 58 and the grinding chamber 39 are held together at 63 by means of a thin bored flange 64 fixed to the shell of T 58 and secured to the grinding chamber 39 by suitable removabe means, such as screws 64. The thin coupling flange 54, as well as the radial flanges surrounding the orifice 57, also act as radiating fins by dissipating operational heat from the grinding chamber 39. Experience has shown that the design of the hopper 56 and the T 58 are quite important to the satisfactory operation of the mill.

Fig. 7 shows a view of the specially designed impeller 67 which is preferably integral with flange 48. This impeller rotates in a suitably sized smooth bore 62 (Fig. 1) and carries the material to be ground to the burrs 45 and 45. The impeller 67 has two similar equally spaced heavy teeth 68, 68 having a long lead angle and Wide similar equally spaced deep grooves 69 and 69' between them so arranged that the material being ground will not be forced by screw-jack action on to the burrs, as would be the case if a single-thread helix with a close lead angle Were used. This plan of an impeller is useful where maize alone is to be ground. The deep wide grooves 69 and 69 provide ample return or refusal channels for the partly ground grist unaccepted by the burrs for finish grinding.

However, careful and intensive investigation and testing revealed that even though the heating and jamming problem of many former mechanically operated burr mills was solved by the double-toothed, equally-grooved impeller previously described, yet another difliculty was discovered. While the heating and jamming had been eliminated, and the maximum production of ground maize obtained for the power consumed as checked by electrical means, yet a much smaller yield of ground product from wheat was obtained than from the maize, and electrical measurements indicated a much lower consumption of electric current by the operating motor of the mill when grinding wheat than when grinding maize. In order to bring the power used for grinding wheat up to that for grinding maize, and to equalize the output of ground product, the differential or selective impeller shown at 72 in Fig. 10 was devised. This impeller 72 has a steeper lead angle than the previously described impeller 67 (Fig. 7) and is made with one wide deep groove 70 and one wide shallow groove 71. The impeller 72 operates in the same bore 62 (Fig. 1) as would the impeller 67 shown in Fig. 7, and in its preferred form, the diameter of the tunnel bore is approximately 2%; inches and the diameter of the impeller is approximately 2% inches. The shallow groove 71 does not carry maize or large seeds to bore 62, but is merely deep enough to allow passage for wheat, rye and other small grains. Grains such as corn or other large seeds are readily carried in the single deep and wide groove 70, which also carries small grains when such are being ground. In effect, the large grains or seeds travel to the burrs by the one deep groove and the small grains or seeds are conveyed to the burrs by both the deep and the shallow grooves 70 and 71, respectively. By carefully working out the proportionate depth and width of the deep and shallow grist-conveying grooves of the difierential or selective'i-mpeller shown in Fig. 8, and the angles thereof, the automatic selective action is very pronounced, whereby the grinding of all food seeds suitable to be ground in the mill is approximately equalized, both in quantity of flour or meal produced, and the measured electric current required to operate the mill. The spiral gears 27 and 2 must also be of the proper ratio in order to secure the most effective results in grinding when the selective impeller 72 (Fig. is incorporated in the mill. The operational application of the selective impeller 72 (Fig. 10) is shown in Fig. 1.

Fig. 12 shows an impeller 72 similar to that shown in Fig. 10, excepting that a circular groove 72 is also provided, which may be useful under certain conditions.

The similar grinding burrs 45 and 45, shown in part in Figs. 1 and 7-8 developed for this grinding mill are made of exceptionally hard and abrasion-resistant Meehanite Metal, Type WH (Ross-Meehan Co. of Chattanooga, Tenn), and are precision-ground on the back and front so as to be parallel, permitting micrometric and therefore accurate adjustment during the operation of the mill. The bottoms of the grooves in the burr 45' in Figs. 7-9 and 13 are specially cut to lie in a plane at right angles to the axis of rotation of the shaft 3. The tops of the teeth are parallel to the plane of the grooves, except for a possible slight chamfer on their inner ends toward the middle of the burr. Both burrs 45 and 45 are similar in construction The burrs 45 and 45 are well adapted to provide equal, accurate and non-distorted grinding action on grist passing between them.

In Fig. 3 platform 74 is secured to bearing flange 75 by any suitable means 75. Bearing flange 75 is integral with bearing body 76 and is secured to housing 1 by appropriate means. Platform 74 supports by means 54' a suitable quiet-running electric motor 54, preferably of the capacitor-start, rubber-mounted, thermostat-protected type, spatially separated from the rest of the mill so that no appreciable amount of operational heat from the motor may be transferred to the housing 1 and grinding chamber 39. Also, any wind-blown flour or meal is substantially eliminated from the ventilating ducts of the electric motor 54. The drive shaft 54a of the electric motor 54 is drivingly connected by a flexible coupling 77 to shaft 28 supporting the driving spiral gears 27. The motor 54 is preferably of a type needing only infrequent oiling and operating satisfactorily at any angle without dripping oil. A suitable safety cover 78 is mounted on the circular end of bearing cap 79 and is also supported by angle bracket 80 bolted both to guard cover 78 and to platform 74.

While there is disclosed only a flexible-shaft coupling between the motor and the gear box, models have been built employing pulley and belt drives therebetween, which arrangement has been entirely satisfactory and possesses certain obvious advantages, such as easy changes in speed, motor size, etc.

In Fig. 3, platform 74 is supported by a cross-member or leg 81 at an angle suitable to prevent the oil in housing 1 from leaking past bearing 29. Leg or crossmember 81 has two feet 82 and 83 provided with holes 84 and 84, respectively, to receive screws for securing the mill to its supporting surface 92a. Cross-member 81 is held in correct standing position by a strut 85 secured to platform 74 at 86 and to cross-member 81 at 87. The control switch 88, preferably of the thermostatic type, is conveniently located on cross-member 81. As best disclosed in Figs, 2 and 3, a third foot 90 may consist of a rounded projectoin attached to housing 1 and resting in a recessed support 91, which may, along with feet 82 and 83, have pieces of felt 92 attached thereunder. The three feet 82, 83 and 90 constitute a stable, self-aligning tripod for sustaining the mill on its supporting surface 92a.

In order to provide thorough lubrication of mechanism in the housing with duereturn of any surplus oil, without dripping, downward through the inclined oil-return channels 42 and 94 to the housing 1, the shafts 3 and 28 are set at angles to the horizontal. The drive shaft 28 in Fig. 3 is preferably disposed at an angle of about 20 degrees and the driven shaft 3 in Fig. 1 is disposed at an angle of about 30 degrees, respectively, to the horizontal. Thorough and long testing have proved these positions to obtain optimum results.

The thrust ball-bearings 19, 119 and 31 are partially immersed in the oil-bath in the housing 1, The operation of the spiral drive gear 27, also immersed in the oil-bath, throws oil over some of the higher working parts inside housing 1. Driven spiral 2 also runs partly in the oil-bath, and, because of its angular plane of operation, picks up and pours oil over hub 22 and thrust ball-bearing 19 (Fig. 1), to insure thorough lubrication. Bearing bushing 30 and collar 32 (Fig. 3), being immersed in the oil-bath, are well lubricated through suitable channels. The lower rear bearing 93 on shaft 3 is also immersed in the oil-bath. Bearing 76 in Fig. 3 is provided with a porous bronze bushing 29 and a sealedon cover 79. An adequate oil-return channel 94 returns any surplus oil to housing 1 at 95. A plug 96 (Fig. l) seals the outer end of shaft bearing 93. Plug 97 (Fig. 1) seals the end of the bore of impeller 72. Plug cap 98 (Fig. 3) seals the end of the bearing support 33. Plate 99 covers inspection opening 100 in housing 1. Bearing bushing 29 (Fig 3) is oiled from the tube having a cap 101. Bearing bushing 41 (Fig. 1) is lubricated at intervals by removing plug 43, or through a capped stand-pipe (not shown) inserted into bearing body 37 in place of plug 43. Bearing 29 at its outer end is above the level of oil in housing 1, obviating the necessity for a stuflingbox which would be needed were the shaft 28 placed horizontally. Experience has shown that stufling-boxes are power-consuming when first tightened in adjustment, and are unreliable later in preventing oil-drip when the oil in housing 1 warms up and consequently thins out during long continued operation of the mill.

Figs. 18 and 19 disclose a modified form of impeller 149 having a recessed driving flange 148 to which is secured the grinding burr by means of a screw 147. The drive shaft extending axially through the bore of the impeller 149 is split into an upper shaft section 197 secured to the impeller 149 by means of the set screw 197a, and the lower shaft section 103 secured to the impeller by means of a screw 150. The shaft sections 197 and 103 are spaced apart and in intimate contact with the spherical bearing 140. As can be seen from the enlarged drawing of Fig. 19, the portion of the bore of the impeller 149 receiving the shaft section 103 gradually tapers outwardly to permit slight variations of angular positions of the shaft section 103 with respect to the impeller 149. Such variable adjustments may be made by regulating the thumb screw 150, in order to adjust the angularity of the face of the burr 145 with the stationary burr 45.

The operation of the grinding mill is very simple and easily understood. To commence grinding operations, the properly plugged T 58 (Fig. 1) and the hopper 56 are filled with dry grain or seeds, suitable for grinding in the mill. A receptacle for the ground product is placed in position under outlet 53. The control barrel 11 (111) is set to the proper position to ensure the coarseness or fineness desired for the product. The mill is now started by the control switch 88 for continuous operation Without any further attention until the grinding is completed. In case a large amount of grinding is done with an extended hopper so that an ordinary-sized receptacle for ground product Would be insuflicient to contain the fines, the mill may be moved to an edge of supporting surface 92a by either supplying an extension to leg 81 and moving foot 90 and support 91 to the edge of the supporting surface, or by moving both foot 82 and foot support 91 to the edge of the supporting surface 920. In either case the outlet 53 will project over the edge of the supporting surface 92a, enabling the employment of a deep receptacle supported in any convenient manner for the ground product. To remove any unwanted grain from the hopper and T receptacle, the plug 59 may be removed by loosening the thumbscrews 61 and 61.

Having thus described my invention, I claim:

1. A grinding mill comprising a grinding chamber, a pair of spaced grinding burrs mounted in said chamber, means for driving one of said burrs to grind material between said burrs, a rotary impeller for feeding said material to said burrs, said impeller comprising a pair of grooves of different uniform depths spiraling continuously in the same direction toward said burrs 2. The invention according to claim 1 in which the depth of one of said grooves is at least twice the depth of the other groove.

3. The invention according to claim 1 in which said driven burr and said impeller are coaxially mounted on a rotary driven shaft, said shaft being inclined to the horizontal with said impeller above said driven burr.

4. The invention according to claim 3 in which said rotary shaft is disposed at an angle of approximately 30 degrees to the horizontal.

5. A grinding mill comprising a supporting frame, a grinding chamber mounted in spaced relation above said frame, a cylindrical feed tunnel above and opening into said grinding chamber, an impeller shaft, bearings mounted on said frame for rotatably supporting said shaft in an inclined position through said grinding chamber and said feed tunnel, a grinding burr st tionarily fixed to said grinding chamber, a rotary grinding burr mounted on said impeller shaft within said grinding chamber and proximately spaced from said stationary burr to grind material therebetween, an impeller for feeding material to said burrs mounted on said shaft concentrically within said feed tunnel, said impeller comprising a pair of grooves of different uniform depths spiraling continuously in the same direction, and means for driving said impeller shaft,

6. The invention according to claim 5 in which the shallower of the two grooves is adapted to feed granular material not substantially larger than the size of wheat, and the deeper groove is adapted to feed granular material not substantially larger than the size of corn.

7. The invention according to claim 5 in which the clearance between the outer surface of the impeller and the inner surface of the feed tunnel is approximately 2-3% of the impeller radius.

8. The invention according to claim 5 in which the width of each groove is at least as wide as its depth and each groove has a substantial lead angle.

9. A grinding mill comprising a supporting frame, a housing containing a reservoir of oil mounted on said frame, a grinding chamber spaced above said housing, a cylindrical feed tunnel above and opening into said grinding chamber, an impeller shaft, bearings rotatably supporting the lower end of said shaft within the oil in said housing, said shaft extending at an angle to the horizontal through said grinding chamber and said feed tunnel, a grinding burr stationarily fixed to said grinding chamber, a rotary grinding burr mounted on said impeller shaft within said grinding chamber and proxi- 10. The invention according to claim 9 in which said driving means comprises a motor mounted on said supporting frame, a drive shaft inclined at an angle to the horizontal driven by said motor, the lower end of said motor shaft being supported in said oil in said housing and drivingly connected to the lower end of said impeller shaft.

11. The invention according to claim 10 in which means are provided for lubricating the portions of the impeller shaft and the drive shaft outside the housing in such a manner that oil gravitates along the shafts toward the housing.

12. The invention according to claim 10 in which the inclination of the impeller shaft is approximately 30 degrees to the horizontal and the inclination of the drive shaft is approximately 20 degrees to the horizontal.

13. The invention according to claim 12 in which said impeller shaft and said drive shaft are disposed in planes substantially normal to each other 14. The invention according to claim 9 in which said impeller shaft comprises an upper section and a lower section separated by a spherical bearing, the lower end of said impeller having a gradually outwardly tapering bore for adjustably receiving the lower section of said shaft.

15. A grinding mill comprising a supporting platform, a motor mounted on one end of said platform and a housing containing a reservoir of oil mounted on the opposite end of said platform, a rotary driv shaft driven at one end by said motor and journaled to rotate within said housing, a foot on said housing and an elevated support member extending transversely of said platform for supporting said mill on a level surface and for inclining said motor and said drive shaft at an angle to said supporting surface, a grinding chamber spaced above said housing, a cylindrical feed tunnel above and opening into said grinding chamber, an impeller shaft journaled in said housing and extending at an angle to said supporting surface through said grinding chamber and said feed tunnel, meshing reduction gears connecting said drive shaft and said impeller shaft for rotation within said oil, a grinding burr stationarily mounted in said grinding chamber, a rotary grinding burr mounted on said impeller shaft and proximately spaced to said stationary grinding burr for grinding material therebetween, an impeller mounted on the upper end of said impeller shaft having a pair of spiral grooves of different uniform depths for uniformly feeding granular material of different sizes to said grinding chamber, an outlet for ground material in said grinding chamber spaced substantially above said level supporting surface, and means for actuating said motor.

16. The invention according to claim 15 in which lever means are provided in said housing for axially adjusting said impeller shaft and the spacing between said burrs.

References Cited in the file of this patent UNITED STATES PATENTS 119,746 Culver Oct. 11, 1871 389,310 Lister et al Sept. 11, 1888 1,947,342 Hess Feb. 13, 1934 2,416,432 Brady Feb. 25, 1947 2,454,406 Rebman Nov. 23, 1948 2,653,770 Vicci Sept. 29, 1953 FOREIGN PATENTS 95,266 Sweden Jan. 26, 1939 

